I might be overexaggerating a bit here, but no matter what spec you are, disc or holy, put your finger on that PoH keybind and press it till it hurts. In most cases (yes, not all, but most) you will be pressing that button for 80% of the fight.

Having done both 10/25 healing in HC I would say like Facerollin mentioned healing is way easier in 25m provided you have decent healers. You wont feel quite as rushed to get that heal, and you have a lot of support. In terms of healing useage, you will be doing a lot of the POH'age :P.